The Snow Spider Trilogy (The Snow Spider; Emlyn's Moon; The Chestnut Soldier) by Jenny Nimmo

The Snow Spider has just been made into a film although the book is much older, written in the 80s I think, and reading the three books was a joy. Although fairly short because written for younger children Nimmo's books don't lack in imagination and they have the ability in spades to send a genuine chill down your spine as the snow spider grants a peek at the crack between worlds.